The vapor storage canisters that are by now standard components in production vehicle fuel systems contain activated carbon that can adsorb vaporized fuel, but which should be protected from direct contact with liquid fuel. Various floats and so called rollover valves are adequate to protect the canister from the direct entry of liquid fuel when the tank is overfilled or tilts excessively. The mixture that collects in the space above the liquid level also contains entrained liquid fuel, however, which can potentially present a problem. The canister may be called upon in future designs to adsorb the large volume of flow that is pushed out of the tank as the tank is filled, the so called fuel fill losses. Fuel fill losses contain a high percentage of entrained liquid fuel, because of the churning effect of the forcefully entering fuel, and separators may be needed to protect the canister carbon bed.
Proposed systems for recovering fuel fill losses use vapor vent valves that route the displaced flow to the canister, but which are closed when the tank is not being filled. Such vapor vent valves are typically incorporated in the fuel tank filler pipe, near the entry point of the filler nozzle, as this is a convenient way to activate various opening and closing mechanisms. They may also be mounted elsewhere, however, so long as they provide an exit path from the vapor space of the fuel tank to the canister, a path that can be selectively opened and closed. Known vapor-liquid separators for tank vapor vent valves are generally somewhat bulky, and not integrated with the vapor vent valve itself. They are also not self limiting, meaning that they do not automatically shutoff and stop flow to the canister when they have separated a given volume of entrained liquid from the flow.